In petroleum refinery operations, oily sludges are produced as a waste product. Such sludges are generally characterized as three-phase, multi-component, organic sludges containing water, oil, and solids. The oil component is typically one or more liquid hydrocarbon fractions of petroleum ranging from gasoline components to heavy oils. The solids component may comprise high boiling organic materials, or carbonaceous solids, and may contain metallic and other inorganic materials. The water is present as a result of the use of water for process cooling, cleaning, or the like. Because of the presence of hazardous materials in such sludges, their disposal presents a problem for the petroleum refiner.
Various methods have been proposed for disposing of oil sludges, but to date none have proven to be entirely satisfactory. One such proposed method involves incineration, but this presents environmental problems, the processing cost is very high, and time and money is required to obtain the necessary permits to operate the process. Another disposal technique is land disposal, involving land fill and surface impoundment.
As pointed out in the paper "Evaluation of Treatment Technologies for Petroleum Refinery Hazardous Wastes" presented at the conference on Performance and Costs of Alternatives to Land Disposal of Hazardous Waste, sponsored by the Air Pollution Control Association on Dec. 8-12, 1986, The Hazardous and Solid Waste Amendments of 1984 (HSWA) state that reliance on land disposal should be minimized or eliminated, and land disposal, particularly land fill and surface impoundment, should be the least favorite method of managing hazardous wastes. Five types of petroleum refinery sludges are identified as being hazardous. These are:
1. Dissolved air flotation (DAF) PA1 2. Slop oil emulsion solids PA1 3. Heat exchange bundle cleaning sludge PA1 4. API separator sludge PA1 5. Tank bottoms (leaded)
Such sludges are considered hazardous because of the presence of metals such as lead and chromium, or organic materials such as benzene, cresols, phenol and the like. As an alternative to land disposal methods, various alternative technologies have been proposed. These include solvent extraction, mechanical dewatering, thermal treatment, chemical fixation and stabilization (mixing the oily sludge with a solidifying agent such as cement). There is, however, a continuing search for a technique of disposing of refinery sludges which both meets environmental regulations and is economic to install and operate.
The United States Environmental Protection Agency, by its 1984 Coke Exemption, has exempted from its standards for fuels to which hazardous wastes have been added petroleum refinery wastes containing oil, provided such wastes are converted into petroleum coke at the same facility at which those wastes were generated, unless the resulting coke product exceeds one or more hazardous waste characteristics.
Due to the severe restriction by the HSWA amendments on land disposal techniques of hazardous waste, various other disposal methods have been proposed. For example, U.S. Pat. No. 3,917,564 discloses a processing technique wherein refinery sludges are used as a quench medium in a delayed coking process wherein the sludge is converted into petroleum coke at a pressure and temperature which cause the hydrocarbons in the sludge to crack and/or polymerize to form coke. While this latter technique may be sometimes satisfactory, not all petroleum refineries include a delayed coker. Further, if the sludge is, for example, very high in undesirable metals and ash, the resulting coke product may not be satisfactory for use as coke.
Thus, while there have been various methods proposed for disposing of petroleum refinery sludges, there is still a need for a simple and inexpensive process to convert such sludges to a coke-like product which is useable as a non-hazardous, non-regulated fuel.
It is also known to distill hydrocarbons from contaminated oil to leave a residue. For example, U.S. Pat. No. 4,101,414 discloses a process wherein used lubricating oil is predistilled in a steam-stripping still and the predistilled used oil is then subjected to vacuum distillation at a temperature below the cracking temperature of the oil to effect a separation of the used lubricating oil from a residue concentrate byproduct of heavy lube oil hydrocarbons and additives. The concentrate product formed during the vacuum distillation step includes heavy lube hydrocarbons, additives, metals, metal compounds and the like and is stated to be useful as a lubrication grease.
It is an obJect of the present invention to provide a process for converting petroleum refinery sludges to a coke-like product which is free, or substantially free, from environmentally undesirable hydrocarbons, e.g. volatile organic compounds, such as benzene, toluene and xylene.
Another object of the invention is such a process which permits treatment of petroleum refinery sludges on-site and leaves non-hazardous waste.
A further object of the present invention is such a process which is simple in operation, does not require substantial and elaborate equipment for carrying out the process, which equipment may be portable, if desired.
An advantage of the present invention is that it does not require extraneous steam for processing and, additionally, a cooling medium, such as cooling water, is not required to cool the coke-like product produced by the process. A further advantage of the invention is that the resulting coke-like product, while meeting environmental requirements, has sufficient BTU content for it to qualify as a low grade petroleum coke, which has an energy value between about 3000 and 10,000 BTU/lb.